Zoom lens and image pickup device including the same

ABSTRACT

A zoom lens includes a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, in order from an object side to an image side. During zooming, the first lens unit is not moved, and the second lens unit, the third lens unit, and the fourth lens unit are moved to change an interval between adjacent lens units. A moving amount m 2  of the second lens unit during zooming from a wide angle end to a telephoto end, a focal length f 2  of the second lens unit, and a focal length fw of a whole system at the wide angle end are each set appropriately.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens, and is particularlysuitable as an image pickup optical system used in an image pickupdevice such as a video camera, a surveillance camera, a digital stillcamera, a broadcast camera, or a silver halide film camera.

2. Description of the Related Art

There is demand for an image pickup optical system in an image pickupdevice to nave a zoom lens with a small size, a wide angle of view, lowaberration, and a high zoom ratio. As a zoom lens that easily achieves ahigh zoom ratio, a positive-dead zoom lens in which a first lens unithaving positive refractive power, a second lens unit having negativerefractive power, a third lens unit having positive refractive power,and a fourth lens unit having positive refractive power are arranged inorder from the object side to the image side is known.

Japanese Patent Application Laid-open No. H8-82743 and U.S. Pat. No.8,284,498 disclose a rear focus type four-unit zoom lens in which thesecond lens unit and the third lens unit are moved for variablemagnification and the fourth lens unit is moved for correction of imageplane changes associated with variable magnification and for focusing.

Such a positive-lead four-unit zoom lens relatively easily achieves ahigh zoom ratio with the whole system being reduced in size. However, inorder to achieve high optical performance over the whole zoom range witha wide angle of view, it is important to appropriately set therefractive power of each lens unit, in particular the refractive powerof the second lens unit, the lens structure of each lens unit, and thelike.

SUMMARY OF THE INVENTION

A zoom lens according to the present invention is a zoom lens including,in order from an object side to an image side: a first lens unit havingpositive refractive power; a second lens unit having negative refractivepower; a third lens unit having positive refractive power; and a fourthlens unit having positive refractive power, wherein during zooming, thefirst lens unit is not moved, and the second lens unit, the third lensunit, and the fourth lens unit are moved to change an interval betweenadjacent lens units, and wherein, the following conditional expressionsare satisfied

−4.9<m2/f2<−3.7

−2.0<f2/fw<−1.5

where m2 is a moving amount of the second lens unit during zooming froma wide angle end to a telephoto end, f2 is a focal length of the secondlens unit, and fw is a focal length of a whole system at the wide angleend.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens sectional diagram, at a wide angle end, of a zoom lensin Embodiment 1.

FIG. 2A is an aberration diagram, at the wide angle end, of the zoomlens in Embodiment 1.

FIG. 2B is an aberration diagram, at an intermediate zoom position, ofthe zoom lens in Embodiment 1.

FIG. 2C is an aberration diagram, at a telephoto end, of the zoom lensin Embodiment 1.

FIG. 3 is a lens sectional diagram, at the wide angle end, of a zoomlens in Embodiment 2.

FIG. 4A is an aberration diagram, at the wide angle end, of the zoomlens in Embodiment 2.

FIG. 4B is an aberration diagram, at the intermediate zoom position, ofthe zoom lens in Embodiment 2.

FIG. 4C is an aberration diagram, at the telephoto end, of the zoom lensin Embodiment 2.

FIG. 5 is a lens sectional diagram, at the wide angle end, of a zoomlens in Embodiment 3.

FIG. 6A is an aberration diagram, at the wide angle end, of the zoomlens in Embodiment 3.

FIG. 6B is an aberration diagram, at the intermediate zoom position, ofthe zoom lens in Embodiment 3.

FIG. 6C is an aberration diagram, at the telephoto end, of the zoom lensin Embodiment 3.

FIG. 7 is a lens sectional diagram, at the wide angle end, of a roomlens in Embodiment 4.

FIG. 8A is an aberration diagram, at the wide angle end, of the zoomlens in Embodiment 4.

FIG. 8B is an aberration diagram, at the intermediate zoom position, ofthe zoom lens in Embodiment 4.

FIG. 8C is an aberration diagram, at the telephoto end, of the zoom lensin Embodiment 4.

FIG. 9 is a schematic diagram or main parts of a video camera (imagepickup device) including a zoom lens according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

The following describes embodiments or a zoom, lens and an image pickupdevice including the same according to the present invention, withreference to the drawings. The zoom lens according to the presentinvention includes a first lens unit having positive refractive power, asecond lens unit having negative refractive power, a third lens unithaving positive refractive power, and a fourth lens unit having positiverefractive power, in order from the object side to the image side.During zooming, the first lens unit is not moved and the second, lensunit, the third lens unit, and the fourth lens unit are moved.

FIG. 1 is a tens sectional diagram, at a wide angle end (short focallength end), of a zoom lens in Embodiment 1 of the present invention.FIGS. 2A, 2B, and 2C are aberration diagrams, respectively at the wideangle end, an intermediate zoom position, and a telephoto end (longfocal length end), of the soon lens in Embodiment 1. The zoom lens inEmbodiment 1 has a zoom ratio of 19.69 and an f-number of 1.35 to 2,38.

FIG. 3 is a lens sectional diagram, at the wide angle end, of a zoomlens in Embodiment 2 of the present invention. FIGS. 4A, 4B, and 4C areaberration diagrams, respectively at the wide angle end, theintermediate zoom position, and the telephoto end, of the zoom lens inEmbodiment 2. The zoom lens in Embodiment 2 has a zoom ratio of 29.59and an f-number of 1.85 to 3.30.

FIG. 5 is a lens sectional diagram, at the wide angle end, of a zoomlens in Embodiment 3 of the present invention, FIGS. 6A, 6B, and 6C areaberration diagrams, respectively at the wide angle end, theintermediate zoom position, and the telephoto end, of the zoom lens inEmbodiment 3. The zoom lens in Embodiment 3 has a zoom ratio of 22.27and an f-number of 1.85 to 2.88.

FIG. 7 is a lens sectional diagram, at the wide angle end, of a zoomlens in Embodiment 4 of line present invention. FIGS. 8A, 8B, and 8C areaberration diagrams, respectively at the wide angle end, theintermediate zoom position, and the telephoto end, of the zoom lens inEmbodiment 4. The zoom lens in Embodiment 4 has a zoom ratio of 19.34and art f-number of 1.85 to 2.88. FIG. 9 is a schematic diagram of mainparts of a video camera (image pickup device) including a zoom lensaccording to the present invention.

The zoom lens in each embodiment is an imaging optical system used in animage pickup device. In the lens sectional diagrams, the left is thesubject side (object side), and the right is the image side. In the lenssectional diagrams, L1 denotes a first lens unit having positiverefractive power, L2 denotes a second lens unit having negativerefractive power, L3 denotes a third lens unit having positiverefractive power, and L4 denotes a fourth lens unit having positiverefractive power. Moreover, SP denotes an aperture stop, which islocated between the second lens unit L2 and the third lens unit L3. Eacharrow indicates the moving locus during zooming from the wide angle endto the telephoto end and the moving direction during focusing.

Though the aperture stop SP is not moved during zooming in the zoom,lens in each embodiment, the aperture stop SP may be movable in anappropriate range. This facilitates further site reduction of the wholesystem. In each embodiment, the aperture stop SP is not moved duringzooming, thus simplifying the image pickup device. P denotes an opticalclock corresponding to an optical filter, a faceplate, or the like. Idenotes an image plane, and corresponds to: an image pickup surface of asolid-state image pickup element such as a CCD sensor or a CMOS sensorin the case where the seem lens is used as an imaging optical system ina digital still camera or a video camera; and a film surface in the casewhere the zoom lens is used in a silver halide film camera.

In the spherical aberration of the aberration diagrams, d denotesd-line, and g denotes g-line. In the astigmatism diagram, ΔM and ΔSrespectively denote a meridional image plane and a sagittal image plane.The lateral chromatic aberration is represented by g-line. Fno denotesan f-number, and ω denotes a half angle of view (degrees). Note that, ineach embodiment, the wide angle end and the telephoto end meanrespective zoom positions when the variable-magnification lens unit islocated at each of both ends of the movable range in the direction ofthe optical axis in the mechanism.

In each embodiment, when zooming from the wide angle end to thetelephoto end, the lens units are moved as indicated by the arrows. Indetail, the second lens unit L2 is moved monotonously toward the imageside. The third lens unit L3 is moved so as to be located more on theobject side at the telephoto end than at the wide angle end, to performvariable magnification.

The fourth lens unit L4 is moved toward the object side in a convexlocus, to correct image plane changes associated with variablemagnification. Moreover, each embodiment employs the rear focus type inwhich the fourth lens unit L4 is moved on the optical axis to performfocusing. A solid curve 4 a and a dotted curve 4 b relating to thefourth lens unit L4 respectively indicate moving loci for correctingimage plane changes associated with zooming when focusing on an objectat infinity and when focusing on a near object. The space between thethird, lens unit L3 and true fourth lens unit L4 is effectively used bymoving the fourth lens unit L4 toward the object side in a convex locus.This enables reduction of the total lens length.

In each embodiment, focusing from an object at infinity to a near objectat the telephoto end is performed by moving the fourth lens unit L4forward, as indicated by an arrow 4 c. In each embodiment, all or partof the third lens unit L3 may be moved in a direction having a componentperpendicular to the optical axis during imaging, to correct blur of acaptured image caused when the zoom lens vibrates, i.e. to perform imageblur correction.

The zoom lens in each embodiment includes the first lens unit L1 havingpositive refractive power, the second ions unit L2 having negativerefractive power, the third lens unit L3 having positive refractivepower, and the fourth lens unit L4 having positive refractive power, inorder from the object side to the image side. During zooming, the firstlens unit L1 is not moved, and the second lens unit L2, the third lensunit L3, and the fourth lens unit L4 are moved to change the intervalbetween adjacent lens units. Let m2 be the moving amount of the secondlens unit L2 during zooming from the wide angle end to the telephotoend, f2 be the focal length of the second lens unit L2, and fw be thefocal length of the whole system at the wide angle end.

In this case, the following conditional expressions are satisfied.

−4.9<m2/f2<−3.7   (1)

−2.0<f2/fw<−1.5   (2).

Here, the moving amount of the lens unit during zooming from the wideangle end to the telephoto end is the difference of the position of thelens unit on the optical axis at the wide angle end and at the telephotoend. The sign of the moving amount of the lens unit is plus when thelens unit is located more on the image side at the telephoto end than atthe wide angle end, and minus when the lens unit is located more on theobject, side at the telephone end than at the wide angle end.

The above-mentioned structure of the zoom lens according to the presentinvention suitable for ensuring a small whole system with a high zoomratio. Decentering the first lens unit L1 is not desirable, because itcauses she field curvature at the telephoto end to be not rotationallysymmetric and, for example, makes the subject distance for focusingdifferent between the left and right of the screen. Accordingly, thefirst lens unit 111 is not moved during zooming. Meanwhile, the secondlens unit L2 and the third lens unit L3 are moved for variablemagnification.

The third lens unit L3 is moved to shorten the entrance pupil positionat the intermediate room position, thereby reducing the front lenseffective diameter. The fourth lens unit L4 is moved to correct imageplane changes associated with variable magnification. Theabove-mentioned conditional expressions (1) and (2) are thus satisfied.

The following describes the technical meanings of the conditionalexpressions (1) and (2). The conditional expression (1) relates to theratio between the difference of the position of the second lens unit L2during rooming from the wide angle one to the telephoto end and thefocal length of the second lens unit L-2. If the upper limit of theconditional expression (1) is exceeded, the third lens unit L1 needs tobe brought closer to the image side at the wide angle end, in order toincrease the difference of the position of the third, lens unit L3 sothat a predetermined zoom ratio is attained. This causes the position ofthe third lens unit L3 and the position of the fourth lens unit L4 to becloser to each other at the wide angle end and as a result causes camsor actuators for driving the third lens unit L3 and the fourth lens unitL4 to approach, making it difficult to arrange them accurately.

If the lower limit is exceeded, on the other hand, the front lenseffective diameter and the total lens length (the distance from thefirst lens surface to the image plane: increase or the negativerefractive power of the second lens unit 12 becomes too high. Thiscauses more changes of field curvature during zooming, which aredifficult to be corrected.

The conditional expression (2) relates to the ratio between the focallength of the second lens unit L2 and the focal length at the wide angleend. If the upper limit of the conditional expression (2) is exceeded,the refractive power of the first lens unit L1 needs to be increased inorder to maintain a predetermined angle of view at the wide angle end.As a result, spherical aberration and axial chromatic aberrationincrease especially in the range from the intermediate zoom position tothe telephoto end, which are difficult to be corrected. If the lowerlimit is exceeded, on the other hand, the front lens effective diameterand the total lens length increase.

Moreover, in the zoom lens according to the present invention, at leastone of the following conditional expressions may be satisfied. Let m3 bethe moving amount of the third lees unit L3 daring zooming from the wideangle end to the telephoto end. Suppose the first lens unit L1 includes,nearest the image side, a lens Glpr having positive refractive power.Let Nlpr be the refractive index of the material of the lens Glpr, andNlpf be the mean value of the refractive indices of the materials of thelenses having positive refractive power included in the first lens unitL1 other than the lens Glpr.

Let N34 n be the mean value of the refractive indices of the materialsof the negative lenses included in the third, lens unit L3 and thefourth lens unit L4, and N34 p be the mean value of the refractiveindices of the materials of the positive lenses included in the thirdlens unit L3 and the fourth lens unit L4. In this case, at least one ofthe following conditional expressions may be satisfied.

−25.0<m2/m3<−2.0   (3)

1.05<Nlpr/Nlpf<1.40   (4)

1.1<N34n/N34p<1.3   (5)

The following describes the technical meanings of the conditionalexpressions. The conditional expression (3) relates to the ratio betweenthe moving amount of the second lens unit L1 during zooming from thewide angle end to the telephoto end and the moving amount of the thirdlens unit L3 during zooming from the wide angle end to the telephotoend.

If the moving amount of the second lens unit L2 decreases and the movingamount of the third lens unit L3 increases and the upper limit of theconditional expression (3) is exceeded, the load of variablemagnification on the third lens unit L3 increases. However, the thirdlens unit L3 is less contributory to variable magnification than thesecond lens unit. Hence, a high zoom ratio is difficult to be attained.If the moving amount of the third lens unit it decreases and the lowerlimit is exceeded, on the other hand, the moving amount of the entrancepupil position decreases due to the movement of the third lens unit L3during zooming. This makes it difficult to reduce the front lenseffective diameter and widen the angle of view.

The conditional expression (4) relates to the ratio between therefractive index of the material of the positive leas Glpr nearest theimage side in the first lens unit L1 and the mean value of therefractive indices of the materials of the positive lenses in the firstlens unit L1 other than the positive lens Glpr nearest the image side.In the first lens unit L1, the angle between the light passing throughthe lenses and the optical axis is at the maximum in the positive lensGlpr nearest the image side. Therefore, the light effective diameterdifference between the lens surface on the object side and the lenssurface on the image side is smaller when the positive lens Glpr nearestthe image side in the first lens unit Id is made thinner. Thisfacilitates reduction of the front lens effective diameter.

However, if the refractive power of the positive lens Glpr nearest, theimage side in the first lens unit L1 is weakened, the light will end uppassing at a steep angle with the optical axis more on the object side,causing an increase in front lens effective diameter, for a smallerfront lets effective diameter, it is effective to increase therefractive index of the material of the positive lens Glpr nearest theimage side in the first lens unit L1 to increase the curvature radius ofthe lens surface, and make the lens thinner while maintaining therefractive power at a predetermined position.

If the upper limit of the conditional expression (4) is exceeded, it isadvantageous to the reduction of the front ions effective diameter, butthe Petzval sum increases and field curvature is difficult to becorrected. If the lower limit is exceeded, on the other hand, the frontlens effective diameter, increases.

The conditional expression (5) defines the ratio between the mean valueof the refractive indices of the materials of the negative lenses in thethird lens unit L3 and the fourth lens unit L4 and the mean value of therefractive indices of the materials of the positive lenses in the thirdlens unit L3 and the fourth lens unit L1. If the refractive index of thematerial of the positive lens decreases and the upper limit of theconditional expression (5) is exceeded, the curvature radius of the lenssurface decreases, causing many nigh-order aberrations. Sphericalaberration, coma aberration, and the like per wavelength are difficultto be corrected. If the lower limit is exceeded, on the other hand,spherical aberration increases at the wide angle end and also fieldcurvature changes more during zooming, which are difficult to becorrected. If is further desirable to specify the numerical ranges ofthe conditional expressions (1) to (5) as follows.

−4.85<m2/f2<−3.80   (1a)

−2.00<f2/fw<−1.55   (2a)

−23.5<m2/m3<−5.5   (3a)

1.08<Nlpr/Nlpf<1.35   (4a)

1.15<N34n/N34p<1.25   (5a).

In the zoom lens according to the present invention, the first lens unitL1 desirably includes one negative lens and at most three positivelenses.

A method of arranging the first lens unit L1 having the same structureas a wide converter on she object side is available for the zoom type inwhich the composite focal, length of the lens units from the second lensunit L2 onward is long, when, reducing the front lens effective diameterin a zoom lens with a wide angle of view and a high zoom ratio. Thismethod, however, increases the total lens length and also increases theweight of the first lens unit L1.

Therefore, in the zoom lens according to the present invention, thefirst lens unit L1 has the above-mentioned structure to reduce the frontlens effective diameter while minimizing increases in the total lenslength and the weight, of the first lens unit L1. If is especiallydesirable that the first lens unit L1 includes one negative lens forachromatism and at most three positive lenses for correction ofspherical aberration, coma aberration, axial chromatic aberration, andthe like mainly at the telephoto end. In the zoom, lens according to thepresent invention, the aperture stop SF is provided between the secondlens unit L2 and the third lens unit L3, and the aperture stop SP is notmoved during zooming.

In the four-unit zoom lens according to the present invention, theaperture stop SP may be disposed between the second lens unit L2 and thethird lens unit L3 or in the third lens unit L3, in order to allowoff-axis light to pass through the aperture even when the aperturediameter of the aperture stop SP is reduced. However, moving theaperture stop SP during zooming requires more actuators or a larger lensbarrel.

In view of this, in the zoom lens according to the present invention,the aperture stop SP is disposed between the second lens unit L2 and thethird lens unit L3, and the aperture stop SP is not moved duringzooming.

As described above, according to each embodiment, it is easy to realizea zoom lens having favorable optical performance and a high zoom ratiowith a small number of lenses even when manufacturing errors are takeninto account.

The following describes the lens structure or each tens unit. The firstlass unit L1 includes a cemented lens in which a negative lens (a lenshaving negative refractive cower) and a positive leas (a lens havingpositive refractive power) are cemented together, and at least onepositive meniscus lens whose surface on the object side is convex, inthe zoom lens in each embodiment, the refractive power of the first lensunit L1 is increased to reduce the size of the whole system. Whenincreasing the refractive power, various aberrations frequently occur inthe first lens unit L1. Especially, spherical aberration frequentlyoccurs on the telephoto side. Accordingly, the positive refractive powerof the first lens unit L1 is shared by the cemented lens and the atleast one positive lens, thus reducing these various aberrations.

The second lens unit L2 has a higher absolute value of the refractivepower on the image side than on the object side, and includes fourindependent lenses, namely, a negative lens whose lens surface on theimage side is concave, two negative lenses, and a positive lens. In thezoom lens in each embodiment, the refractive power of the second lensunit. L2 is increased to reduce the effective diameter of the first lensunit L1 while ensuring a wide angle of view at the wide angle end.

When increasing the refractive power of the second lens unit L2, variousaberrations frequently occur in the second lens unit L2. Especially,field curvature and lateral chromatic aberration frequently occur on thewide angle side. In each embodiment, the negative refractive power ofthe second lens unit L2 is shared by the three negative lenses. Inaddition, lateral chromatic aberration is reduced by the positive lens.Such a lens structure enables a smaller front lens effective diameterand high optical performance to be achieved with a wide angle of view.

The third lens unit L3 includes a positive lens whose lens surface onthe object side is convex, a negative lens, and a positive lens. In thezoom lens in each embodiment, the refractive power of the third lensunit L3 is increased to reduce the moving amount (the difference of theposition) during rooming while reducing the total isms length at thewide angle end. When increasing the refractive power, variousaberrations frequently occur in the third lens unit L3. Especially,axial chromatic aberration arid coma alter rat lot; frequently occur,

Accordingly, the power of the third lens unit L3 is shared by the twopositive lenses and the negative lens, and also one lens surface of thefirst positive lens from the object side is aspherically shaped toreduce coma aberration. Besides, a low-dispersion material (whose Abbenumber is greater than or equal to 70) is used, as the material of thesecond positive lens from the object side, to reduce axial chromaticaberration.

The fourth lens unit L4 includes a cemented fens in which a positivelens and a negative lens are cemented together. In each embodiment, thecemented lens structure of the fourth lens unit L4 reduces lateralchromatic aberration and field curvature changes during zooming.

In each embodiment, the above-mentioned structure of each lens unitenables obtainment of a zoom lens whose whole system is small and thatsupports a wide angle of view, i.e. an imaging angle of view of 65 to72° at the wide angle end, and a high zoom ratio, i.e. a zoom ratio ofabout 19 to 30. When the zoom lens in each embodiment is used in artimage pickup device, distortion aberration from among variousaberrations may be corrected by electrical image processing. Inparticular, the front lens effective diameter can be easily reduced bysetting the image pickup range on the wide angle side to be small withrespect to the maximum image pickup range and correcting theabove-mentioned distortion aberration.

In the zoom lens according to the present invention, the effective imagediameter at the wide angle end may be smaller than the effective imagediameter at the telephoto end.

The following shows Numerical Examples 1 to 4 respectively correspondingto Embodiments 1 to 4. In each numerical example, i denotes the ordinalposition of a surface from, the object side, ri denotes the curvatureradius of the ith surface, di denotes the interval between the ithsurface and the (i+1)th surface, and ndi and vdi respectively denote therefractive index and the Abbe number of the material of the ith opticalmember with respect to d-line.

In Numerical Examples 1 to 4, two surfaces nearest the image side areeach a plane corresponding to an optical block. BF denotes back focus,which is an air-converted distance from the last lens surface to theimage plane. Regarding an aspherical surface, let X be a displacement inthe direction of the optical axis at a height H from the optical axiswith respect to a surface vertex. The light travel direction is set topositive. Let R be a paraxial curvature radius, k be a conic constant,and A4 and A6 be aspherical coefficients. In this case, X is given bythe following expression.

$X = {\frac{H^{2}/R}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( {H/R} \right)^{2}}}} + {A\; 4\; H^{4}} + {A\; 6\; H^{6}}}$

Here, * denotes a surface having an aspherical shape, and “e-z” denotes10^(−x). The angle of view is calculated at tan⁻¹(y/f) where y is theimage height and f is the focal length. Table 1 shows the relationsbetween the above-mentioned conditional expressions and the numericalvalues in the numerical examples.

NUMERICAL EXAMPLE 1

Unit mm Surface data Surface number r d nd νd  1 78.363 1.55 1.8547824.8  2 30.860 6.28 1.59282 68.6  3 −308.803 0.20  4 30.208 3.59 1.8348142.7  5 100.485 (variable)  6 248.972 0.80 1.91082 35.3  7 7.731 3.28  8−42.970 0.65 1.83481 42.7  9 30.582 1.39 10 −21.227 0.60 1.83481 42.7 11−394.864 0.17 12 29.903 2.14 1.95906 17.5 13 −40.022 (variable) 14(stop) ∞ (variable) 15* 9.641 3.17 1.58313 59.4 16 −195.002 4.23 1733.596 0.60 2.00100 29.1 18 8.880 0.44 19* 12.155 2.19 1.55332 71.7 20−164.942 (variable) 21 13.336 3.19 1.63654 55.4 22 −17.040 0.60 1.8465623.9 23 −55.163 (variable) 24 ∞ 1.97 1.51633 64.1 25 ∞ Image plane ∞Aspherical surface data 15th surface K = −1.03637e+000 A4 = 5.15644e−005A6 = 8.02003e−008 19th surface K = −7.32904e−001 A4 = −2.11685e−005 A6 =5.90416e−007 Various data Zoom ratio 19.69 Wide angle IntermediateTelephoto Focal length 3.78 28.09 74.43 F-number 1.85 2.68 2.88 Halfangle of view 36.07 5.60 2.12 (degrees) Image height 2.75 2.75 2.75Total lens length 87.68 87.68 87.68 BF 9.33 14.84 9.68 d5 0.94 23.2928.88 d13 29.83 7.48 1.90 d14 7.64 2.85 2.85 d20 4.84 4.12 9.28 d23 7.0412.55 7.39 Zoom lens unit data Unit Starting surface Focal length 1 141.95 2 6 −7.34 3 14 ∞ 4 15 23.08 5 21 19.79 6 24 ∞

NUMERICAL EXAMPLE 2

Unit mm Surface data Surface number r d nd νd  1 156.468 1.65 1.8061033.3  2 48.625 5.92 1.43700 95.1  3 −179.010 0.17  4 65.127 2.83 1.4970081.5  5 432.018 0.17  6 35.270 4.29 1.59522 67.7  7 139.631 (variable) 8 220.919 0.66 1.88300 40.8  9 7.915 3.10 10 487.280 0.60 2.00069 25.511 50.122 1.30 12 −21.009 0.60 1.91082 35.3 13 42.671 0.17 14 23.4552.02 2.10205 16.8 15 −73.508 (variable) 16 (stop) ∞ (variable) 17*11.018 3.24 1.58313 59.4 18 −217.714 3.64 19 −97.507 0.60 1.80610 33.320 12.376 0.52 21* 18.354 2.21 1.55332 71.7 22 −29.919 (variable) 2315.788 3.01 1.59522 67.7 24 −14.064 0.60 1.90366 31.3 25 −29.892(variable) 26 ∞ 1.97 1.51633 64.1 27 ∞ Image plane ∞ Aspherical surfacedata 17th surface K = −2.48235e−001 A4 = −1.62827e−005 A6 =−1.20469e−007 21st surface K = −5.88650e+000 A4 = 3.74746e−005 A6 =−5.23611e−007 Various data Zoom ratio 29.59 Wide angle IntermediateTelephoto Focal length 3.90 42.44 115.42 F-number 1.85 2.94 3.30 Halfangle of view 35.23 3.71 1.37 (degree) Image height 2.75 2.75 2.75 Totallens length 105.99 105.99 105.99 BF 10.22 17.44 9.45 d7 0.83 33.21 38.15d15 38.98 6.60 1.66 d16 6.55 3.86 3.09 d22 12.11 7.59 16.35 d25 7.9315.15 7.15 Zoom lens unit data Unit Starting surface Focal length 1 151.74 2 8 −7.76 3 16 ∞ 4 17 26.55 5 23 22.10 6 26 ∞

NUMERICAL EXAMPLE 3

Unit mm Surface data Surface number r d nd νd  1 80.533 1.63 1.8061033.3  2 35.312 6.55 1.43700 95.1  3 −731.128 0.16  4 66.197 2.31 1.4970081.5  5 239.131 0.17  6 31.288 4.12 1.59522 67.7  7 188.277 (variable) 8 117.072 0.62 1.88300 40.8  9 7.241 3.20 10 −348.351 0.60 2.00069 25.511 78.155 1.12 12 −18.328 0.60 1.91082 35.3 13 35.258 0.17 14 22.3201.92 2.10205 16.8 15 −63.226 (variable) 16 (stop) ∞ (variable) 17* 9.7313.37 1.58313 59.4 18 −72.681 2.96 19 526.078 0.60 1.80610 33.3 20 8.7890.85 21* 11.845 2.14 1.55332 71.7 22 −62.598 (variable) 23 15.631 3.151.59522 67.7 24 −12.878 0.60 1.90366 31.3 25 −27.059 (variable) 26 ∞1.97 1.51633 64.1 27 ∞ Image plane ∞ Aspherical surface data 17thsurface K = −4.50803e−001 A4 = −1.33946e−005 A6 = −2.84777e−007 21stsurface K = −1.31826e+000 A4 = 2.06647e−005 A6 = 1.32008e−006 Variousdata Zoom ratio 22.27 Wide angle Intermediate Telephoto Focal length3.94 38.76 87.68 F-number 1.85 2.68 2.88 Half angle of view 34.97 4.061.80 (degrees) Image height 2.75 2.75 2.75 Total lens length 95.72 95.7295.72 BF 8.94 16.20 10.62 d7 0.66 28.95 33.27 d15 34.24 5.95 1.64 d164.56 3.17 3.11 d22 10.48 4.62 10.25 d25 6.64 13.90 8.33 Zoom lens unitdata Unit Starting surface Focal length 1 1 46.74 2 8 −7.09 3 16 ∞ 4 1722.97 5 23 21.44 6 26 ∞

NUMERICAL EXAMPLE 4

Unit mm Surface data Surface nuraber r d nd νd  1 53.156 1.29 2.0006925.5  2 34.139 4.62 1.43700 95.1  3 −804.569 0.17  4 32.500 3.35 1.4387594.9  5 116.329 0.17  6 44.909 1.82 1.88300 40.8  7 89.988 (variable)  8120.894 0.60 1.95375 32.3  9 7.651 2.84 10 63.868 0.60 1.83481 42.7 1126.578 1.60 12 −16.232 0.60 1.71300 53.9 13 25.881 0.17 14 20.245 1.792.10300 18.1 15 −100.309 (variable) 16 (stop) ∞ (variable) 17* 10.3743.64 1.58313 59.4 18 −73.078 3.49 19 −77.487 0.60 1.91082 35.3 20 10.2330.46 21* 11.144 2.64 1.55332 71.7 22 −25.870 (variable) 23 16.078 2.921.59522 67.7 24 −14.750 0.60 2.00100 29.1 25 −28.599 (variable) 26 ∞1.97 1.51633 64.1 27 ∞ Image plane ∞ Aspherical surface data 17thsurface K = −3.95101e−001 A4 = −7.22781e−006 A6 = −1.67185e−007 21stsurface K = −1.49619e+000 A4 = −5.51867e−007 A6 = 7.68037e−007 Variousdata Zoom ratio 19.34 Wide angle Intermediate Telephoto Focal length4.33 37.32 83.84 F-number 1.85 2.68 2.88 Half angle of view 32.43 4.221.88 (degrees) Image height 2.75 2.75 2.75 Total lens length 94.99 94.9994.99 BF 8.94 16.59 12.16 d7 1.24 27.12 31.07 d15 32.11 6.23 2.28 d166.21 4.09 3.10 d22 12.52 6.98 12.41 d25 6.64 14.30 9.86 Zoom lens unitdata Unit Starting surface Focal length 1 1 44.92 2 8 −6.94 3 16 ∞ 4 1723.22 5 23 27.79 6 26 ∞

TABLE 1 Conditional Numerical Example expression 1 2 3 4 (1) −3.805−4.808 −4.600 −4.300 (2) −1.942 −1.990 −1.800 −1.600 (3) −5.833 −10.789−22.434 −9.574 (4) 1.152 1.087 1.087 1.310 (5) 1.209 1.176 1.176 1.240

The following describes an example of an image pickup device (videocamera) that uses the zoom lens according to the present invention as animaging optical system, with reference ho FIG. 9.

In FIG. 9, a video camera main body 10 is a main body of the videocamera. An imaging optical system 11 includes the zoom lens described inany of Embodiments 1 to 4. A solid-state image pickup element 12 such asa CCD sensor or a CMOS sensor is included in the camera main body, andreceives a subject image ferried by the imaging optical system 11. Amemory 13 records information corresponding to the subject imagephotoelectrically converted by the solid-state image pickup element 12.An electronic viewfinder 14 is used to observe the subject imagephoto-electrically converted by the solid-state image pickup element 12.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-066107, filed Mar. 27, 2013, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A zoom lens comprising, in order from an object side to an image side: a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit, having positive refractive power; and a fourth lens unit having positive refractive power, wherein during zooming, the first lens unit is not moved, and the second lens unit, the third lens unit, and the fourth lens unit are moved to change an interval between adjacent lens units, and wherein the following conditional expressions are satisfied −4.9<m2/f2<−3.7 −2.0<f2/fw<−1.5 where m2 is a moving amount of the second lens unit during zooming from a wide angle end to a telephoto end, f2 is a focal length of the second lens unit, and fw is a focal length of a whole system at the wide angle end.
 2. The zoom lens according to claim 1, wherein the following conditional, expression is satisfied −25.0<m2/m3<−2.0 where m3 is a moving amount of the third lens unit during zooming from the wide angle end to the telephoto end.
 3. The zoom lens according to claim 1, wherein the first lens unit includes one negative lens and at most three positive lenses.
 4. The room lens according to claim 1, wherein the second lens unit includes a negative lens, a negative lens, a negative lens, and a positive lens, in order from, the object side to the image side.
 5. The room fens according to claim 1, comprising an aperture stop between the second lens unit and the third lens unit, wherein the aperture stop is not moved during zooming.
 6. The zoom lens according to claim 1, wherein the following conditional expression is satisfied 1.05<Nlpr/Nlpf<1.40 where the first lens unit includes, nearest the image side, a lens Glpr having positive refractive power, Nlpr is a refractive index of a material of the lens Glpr, and Nlpf is a mean value of refractive indices of materials of lenses having positive refractive power in the first lens unit other than the lens Glpr.
 7. The zoom lens according to claim 1, wherein the following conditional expression is satisfied 1.1N34n/N34p1.3 where N34 n is a mean value of refractive indices of materials or negative lenses included in the third lens unit and the fourth lens unit, and N34 p as a mean value of refractive indices of materials of positive lenses included in the third lens unit and the fourth lens unit.
 8. An image pickup device comprising: a zoom lens; and an image pickup element for receiving an image formed by the room, lens, wherein the zoom lens comprises, in order from an object side to an image side: a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit having positive refractive power; and a fourth lens unit having positive refractive power, wherein during zooming, the first lens unit is not moved, and the second lens unit, the third tens unit, and the fourth lens unit are moved to change an interval between adjacent lens units, and wherein the following conditional expressions are satisfied −4.9<m2/f2<−3.7 −2.0<f2/fw21 −1.5 where m2 is a moving amount of the second lens unit during zooming from a wide angle end to a telephoto end, f2 is a focal length of the second lens unit, and fw is a focal length of a whole system at the wide angle end. 